1. Field of the Invention
This invention relates to an imaging apparatus having the function of displaying an image of an object on a finder in real-time.
2. Description of the Related Art
A digital still camera retrieves image data obtained by a CCD image sensor into a DRAM or a flash memory and subsequently transfers the image data to a so-called personal computer or the like. A major proportion of this type of the digital still camera has hitherto been of the type coping with the video graphics array (VGA) system.
Referring to FIG. 1, this digital still camera 200 includes a CCD image sensor 201 for generating image signals, an input processing/image processing circuit 202, a memory controller 203 for reading and writing image data, an output processing circuit 204 for conversion to an output image of a pre-set system, a finder 205 for displaying the state of an object at the time of image shooting, a recording unit 207 for recording compressed image data over a CPU bus 206 and a compression/expansion circuit 208 for compressing/expanding image data. The digital still camera 200 also includes a memory 209, formed by, for example, a DRAM, and a CPU 210 for controlling the overall device.
Before starting the image shooting of an object, the user has to confirm an object image displayed on the finder 205. This state is termed a finder mode. At this time, the CCD image sensor 201 sends image signals obtained on photoelectric conversion of the imaging light from an object to the input processing/image processing circuit 202. The input processing/image processing circuit 202 performs the correlated dual sampling processing on the image signals to digitize the image signals. The input processing/image processing circuit 202 then performs pre-set signal processing, such as gamma correction, knee processing or camera processing and routes the processed image signals to the memory controller 203, which then is responsive to the control by the CPU 210 to send the image data from the input processing/image processing circuit 202 to the output processing circuit 204. The output processing circuit 204 encodes image data in accordance with, for example, the National Television System Committee (NTSC) system, and analogizes the encoded image data to route the resulting analog data to the finder 205. This allows the object as an object of image shooting to be indicated on the finder 205.
On the other hand, if the user pushes a shutter button, not shown, to shift to the recording mode, the memory controller 203 causes the image data furnished from the input processing/image processing circuit 202 to be written in the memory 209. The CPU 210 causes the image data to be read out from the memory 209 and compresses the image data from the recording unit 207 in the compression/expansion circuit 208 in accordance with, for example, the Joint photographic Experts Group (JPEG) system to record the compressed image data in the recording unit 207.
If the user performs pre-set processing to shift to the reproducing mode, the CPU 210 causes image data to be read out from the recording unit 207 to cause the image data to be expanded in JPEG system in the compression/expansion circuit 208 to route the resulting data via memory controller 203 and output processing circuit 204 to the finder 205. This causes the as-shot image to be displayed on the finder 205.
In keeping up with recent outstanding technical progress in the CCD image sensor, the resolution of image data is approximately surpassing 1,000,000 pixels. On the other hand, it may be feared that the digital still camera of the above-described structure cannot sufficiently cope with the image data exceeding 1,000,000 pixels.
If, for example, the CCD image sensor 201 outputs image signals of high resolution in the finder mode, the input processing/image processing circuit 202 has to perform resolution conversion of image data in real-time in meeting with the resolution of the finder 205. Simultaneously, the memory controller 203 has to access the memory 209. The output processing circuit 204 also has to perform pre-set processing.
The result is stagnancy on the CPU bus 106, such that each circuit cannot execute pre-set processing in real-time and hence an image of an object is displayed in a frame-decimated fashion on the finder 205. If, in this case, an object has made movements, there is produced deviation between the actual object and the movement of the object displayed on the finder 105, thus producing an inconvenience in the imaging operation.
On the other hand, if image data is not of high resolution, the resolution of the image data has to be converted into that of, for example, the NTSC system or the PAL system, taking into account the system of the finder 205. In this case, it is similarly required to display an image on a finder in real-time.